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<head><meta charset="utf-8"><title>Bisect performance regression · t-compiler · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/index.html">t-compiler</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html">Bisect performance regression</a></h3>

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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204711304" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Gary Guo <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204711304">(Jul 22 2020 at 19:27)</a>:</h4>
<p>Is there a way to locate a specific commit for performance regression?  <a href="https://github.com/rust-lang/rust/issues/74615">#74615</a> shows a quite drastic stable-to-stable performance regression, and it seems that cargo bisect-rustc cannot deal with performance regression</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204715485" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204715485">(Jul 22 2020 at 20:03)</a>:</h4>
<p>if you know the asm you're looking for (or the one you don't want) you could still use cargo-bisect-rustc with a custom script runner to grep the emitted .S file for your example</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204718041" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Jake Goulding <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204718041">(Jul 22 2020 at 20:23)</a>:</h4>
<p><span class="user-mention" data-user-id="116113">@lqd</span> straight to the assembly? Hardcore.</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204718148" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204718148">(Jul 22 2020 at 20:24)</a>:</h4>
<p>if a benchmark is stable enough it's true you could grep + hyperfine :)</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204718212" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204718212">(Jul 22 2020 at 20:24)</a>:</h4>
<p>or even manually mark the bisection bounds with the tool</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204726484" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204726484">(Jul 22 2020 at 21:45)</a>:</h4>
<p>eh my bet is: check the llvm upgrades in that range</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204726742" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204726742">(Jul 22 2020 at 21:48)</a>:</h4>
<p>there was also <a href="https://github.com/rust-lang/rust/issues/74183">https://github.com/rust-lang/rust/issues/74183</a> which was very similar</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204756818" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Gary Guo <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204756818">(Jul 23 2020 at 03:12)</a>:</h4>
<p><a href="https://github.com/rust-lang/rust/issues/74183">#74183</a> looks similar, but that does not compile in 1.37 so I couldn't confirm if they are from the same root cause.</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/131828-t-compiler/topic/Bisect%20performance%20regression/near/204798713" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Xavier Denis <a href="https://rust-lang.github.io/zulip_archive/stream/131828-t-compiler/topic/Bisect.20performance.20regression.html#204798713">(Jul 23 2020 at 13:47)</a>:</h4>
<p>the mir emitted from 1.37 and 1.38 are the same <a href="https://rust.godbolt.org/z/eh4ajq">https://rust.godbolt.org/z/eh4ajq</a></p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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